Numerous devices have been proposed for constituting a heart ventricle prosthesis. They are generally peristaltic-type pumps, i.e. they include a deformable pocket connected to the blood circulation path via an inlet valve and an outlet valve. The pocket is compressed by applying an external force thereto, generally by means of a pneumatic device under the control of a source of pressure.
From the physiological point of view, this type of pump behaves similarly to the natural heart (which is a contractile pocket), thereby obtaining the essential advantage of practically eliminating the phenomenon of hemolysis (i.e. the destraction of red globules), by considerbaly reducing phenomena of shock, turbulence, abrupt pressure variation, . . . in the blood fluid. The pocket is deformed by externally applied stress. It thus contains no internal moving member such as a piston in direct contact with the blood.
Another advantage of peristaltic pumps is that they always operate with blood admission at zero or slightly negative pressure. This thus avoids any risk of collapsus in the event of insufficient venous return. Such risks are capable of causing a pump to operate wrongly and to cause the patient to die quickly by crushing the auricular cavity and/or the vessels, and they are inherent to displacement-type pumps which therefore require either to control the flow-rate very accurately to the blood pressure, or else they require a buffer volume, which can only be provided outside the body because of the resulting extra bulk.
However, in prior proposals, pneumatic drive is an obstacle to providing a prosthesis which is completely implantable and autonomous. Firstly, the pneumatic device is voluminous (a source of pressure, electrically controlled valves, and a pneumatic regulator device) thus requiring apparatus outside the patient and connected to the patient by pneumatic links.
Then, and most particularly, the overall efficiency of a pneumatic compressor is low, thus requiring a high power source of electrical energy. Such sources are heavy and voluminous, and above all because of the low efficiency of the electro-pneumatic conversion, they generate large quantities of heat which is incompatible with the human body's thermoregulation system.
Finally, a pneumatically driven heart uses thin diaphragms (for transforming the pneumatic energy supplied into mechanical pumping energy), which are particularly exposed to the risk of rupture, in particular following spots of calcification which weaken the diaphragm wall.
Preferred implementations of the present invention provide a heart pump which mitigates these drawbacks.
The pump in accordance with the invention is of the peristaltic type, thereby benefitting from the advantages related to the absence of a moving member inside the pocket (and thus a very low degree of hemolysis), and to non-displacement operation (thereby avoiding the risk of venous collapse).
One of the aims of the present invention is to provide an entirely implantable and autonomous prosthesis for a ventricle or a heart. Because of the excellent efficiency of an assembly for converting electrical energy into mechanical pumping energy, it is possible to limit the energy consumption of an electrically driven prosthesis to values which are compatible with small sources of electricity (batteries or isotope cells) which could be implanted, or which could at any rate be conveniently carried by the patient in such a manner as to enable the patient to move about freely.
The excellent efficiency also makes it possible to limit the heat dissipation to values which are compatible with natural thermoregulation. It is shown that the total power consumed by the pump (developed mechanical power+heat losses) is of the same order of magnitude as the theoretical physiological power of a natural heart.
Further, the disposition of the various components constituting a pump in accordance with the invention make it possible, without reducing performance, to provide a pump having an overall shape and size similar to those of a natural organ. This compact disposition facilitates the implantation of one or two artificial organs.
It is also shown that the pump has a degree of flexibility enabling it to absorb the movements of the thorax (breathing, coughing) in the same manner as a natural heart. This avoids certain difficulties which are encountered when a rigid organ is implanted, as has been the case in certain prior art proposals.
Finally, it will be shown that in addition to the possibility of servocontrolling the pump regime (flowrate, frequency, waveform) to blood pressure, the very structure of the pump provides automatic adaptation. In other words, if the blood pressure increases the volume of the ventricle tends to increase due to elastic deformation. Under such conditions, and without any change in the heart frequency nor in the form of the pressure wave, the volume output at each contraction increases, thereby improving the irrigation of the patient. In this case, the prosthesis has higher performance than the natural organ since the natural tissues do not allow the ventricle to dilate under the effect of an increase in blood pressure.